Its pretty flowers can turn a riverbank rosy pink, but despite its good looks; Himalayan balsam is an aggressive alien that needs to be stopped in its tracks.
On Saturday 28 June, 200 people will be turning out to do just that – and help clear the River Nadder from this garden escapee before it swamps the river valley.
And they are not the only ones to blitz the balsam – throughout the summer other volunteer work parties will tackle the plant at locations as far a field as Hampshire to ensure the River Avon, through which it flows, and tributaries like the Nadder, are rescued from its grip.
Himalayan Balsam (impatiens glandulifera) is also known as Policeman’s Helmet and is a native of the Nepalese mountains. It can grow up to two metres tall, and was first grown in gardens over 100 years ago. Its ability to hurl its seeds with great force by means of a coiled spring mechanism within the seed-pod makes it virtually unstoppable once it has set seed and now it infests riverbanks across the nation and is a real threat to the wildlife.
“Himalayan balsam grows rapidly, smothering and shading the riverbanks and clogging up drainage ditches. It crowds out native wetland plants, which are important food sources for insects. Most of our own insects do not feed on balsam and so they stay away. An absence of insects means that the whole balance of the river ecology can be damaged,” says Martin de Retuerto, the Wessex Chalk Streams project officer, who is leading the invasive plant strategy in Wiltshire through the Wiltshire Wildlife Trust.
“Balsam spreads quickly due to the way that rivers and floodplains interconnect, and once in the wild they can cover whole areas of wetlands in a matter of months. At the moment we can still do something about it, but in another ten years there may be no hope of controlling this pest,” says Martin.
So the race is on to clear stretches of the Nadder, where a blanket of Himalayan balsam is about to flower, and just about to form the rocket-fuelled seed-pods. Fortunately the balsam, despite towering over people’s heads, is very easy to pull up.